Autophagy is required during high MUC2 mucin biosynthesis in colonic goblet cells to contend metabolic stress

Goblet cells are specialized for the production and secretion of MUC2 glycoproteins that forms a thick layer covering the mucosal epithelium as a protective barrier against noxious substances and invading microbes. High MUC2 mucin biosynthesis induces endoplasmic reticulum (ER) stress and apoptosis in goblet cells during inflammatory and infectious diseases. Autophagy is an intracellular degradation process required for maintenance of intestinal homeostasis. In this study, we hypothesized that autophagy was triggered during high MUC2 mucin biosynthesis from colonic goblet cells to cope with metabolic stress. To interrogate this, we analyzed the autophagy process in high MUC2-producing human HT29-H and a clone HT29-L silenced for MUC2 expression by lentivirus-mediated shRNA, and WT and CRISPR/Cas9 MUC2 KO LS174T cells. Autophagy was constitutively increased in high MUC2-producing cells characterized by elevated pULK1S555 expression and increased numbers of autophagosomes as compared with MUC2 silenced or gene edited cells. Similarly, colonoids from Muc2 thorn / thorn but not Muc2-/ littermates differentiated into goblet cells showed increased autophagy. IL-22 treatment corrected misfolded MUC2 protein and alleviated the autophagy process in LS174T cells. This study highlights that autophagy plays an essential role in goblet cells to survive during high mucin biosynthesis by regulating cellular homeostasis. NEW & NOTEWORTHY It is unclear how colonic goblet cells survive by producing high output MUC2 mucin that triggers endoplasmic stress by misfolded MUC2 proteins. To cope with metabolic stress, we interrogated if autophagy played an essential role in regulating cellular homeostasis. Indeed, high MUC2 mucin biosynthesis dysregulated autophagy processes that was regulated by IL-22 to maintain gut barrier innate host defenses.

Automated summary

This study reveals that autophagy plays a crucial role in regulating cellular homeostasis in goblet cells during high mucin biosynthesis. Additionally, IL-22 treatment can correct misfolded MUC2 proteins and alleviate the autophagy process in cells.